1. Field of the Invention
The present invention relates to an ink jet recording apparatus. In particular, the present invention relates to an ink jet recording apparatus, and an ink jet recording method therefor, for performing the ejection control of a recording head.
2. Description of the Related Art
As an example of an apparatus for performing a recording using a recording head including a plurality of recording elements, an ink jet recording apparatus having a plurality of ejection openings for ejecting ink has been known.
In order to keep ink ejection stability and/or constant ink ejection amount in the ink jet recording apparatus, the temperature of ink in the recording head is one of very important parameters. Specifically, ink properties such as the viscosity or surface tension change depending on the ink temperature. The ejection status also changes depending on the change of the ink property. Ink viscosity is particularly high in a low temperature environment, which may cause the ejection to be unstable to deteriorate the recording quality. In order to always maintain stabilized ejection, ink in the apparatus in some cases is heated to have a predetermined temperature when the recording is started. To achieve this, such a structure is frequently employed that heaters are provided at the interior and/or exterior of the recording head. When ink is not ejected for a long time period, solvent in the vicinity of the ejection opening evaporates to increase the ink viscosity, which inevitably causes the deterioration of the ejection status when the ejection is resumed. To get long the maximal time between a time prior has been completed and a time the next ejection can be performed in a preferred status (hereinafter referred to as “first-ejection time”), a recovery operation such as a preliminary ejection is performed, in the middle of the recording or prior to the start of the next recording, by ejecting a certain amount of ink outside the recording medium until ink can be ejected correctly.
For example, Japanese Patent Application Laid-Open No. 3-234629 (1991) discloses a structure in which, until a head temperature reaches a predetermined temperature after the apparatus power source is turned on, a driving pulse applied to the head is changed depending on the head temperature to warm-up the apparatus. Another structure is disclosed in Japanese Patent Application Laid-Open No. 4-070348 (1992) in which, in order to increase the head temperature to a fixed temperature more rapidly, an electrothermal transducer element (ejection heater) for generating thermal energy used for ink ejection is applied, depending on a temperature detected at the turning ON of the power source or the cancellation of the preheating, with an electric signal at which ink is not ejected so that the element generates heat.
Representative ink jet recording apparatuses include: the serial type one in which a recording head is scanned on a recording medium in a predetermined direction to perform recording; and the full line type one in which a recording head having a width equal to or larger than the width of the recording medium (hereinafter referred to as “line head”) is used to perform recording. The line head does not scan a recording medium as in the case of the serial type recording head and performs recording to the recording medium on the line basis. Thus, the line head requires a shorter time for recording a predetermined amount when compared to the case of the serial type one and has a main objective of a high-speed recording.
The preliminary ejection in the serial type recording apparatus is frequently performed in places for the preliminary ejection that are provided exterior to the recording region (e.g., cap, preliminary ejection receipt). Thus, when the preliminary ejection must be performed in the middle of recording, the recording head is once moved to outside the recording region to perform a preliminary ejection, during which the recording is interrupted. As a result, a time required for recording a predetermined amount is increased. Furthermore, the ejected ink is waste ink, thus increasing, when the preliminary ejection is performed with a higher frequency, the amount of waste ink.
The full line type recording apparatus, having the main objective of providing a high-speed printing as described above, is desirably prevented from having a lower recording rate as much as possible. In view of the above, the present applicant suggests a mechanism through which a preliminary ejection is not performed outside the recording region but is performed on a belt for transporting a recording medium. However, the mechanism in which the preliminary ejection is performed on a belt requires the belt to be cleaned because ink left on the belt contaminates the recording medium. This belt cleaning is performed as required in the middle of the recording, thus causing the time required for the recording to be prolonged in order to provide the cleaning. Ink preliminarily ejected to the belt is waste ink as in the case of the serial type one.
As described above, in both of the serial type one and the full line type one, the larger the number of preliminary ejections in the middle of the recording, the longer the period required for printing. Also, the larger the number of preliminary ejections, the more the amount of waste ink. Thus, in order to realize a high-speed recording with reduced wasteful ink consumption, the number of times at which the preliminary ejection is performed has been required to be reduced.
In order to reduce the number of times at which the preliminary ejection is performed, the recording head is desirably provided with a status favorable for ink ejection as long as possible. Specifically, if the first-ejection time becomes longer, the number of times at which the preliminary ejection can be reduced. An effective method for providing such a long first-ejection time is to adjust, during the recording operation, the temperature of the recording head to prevent the ink temperature in the head from being increased or reduced more than necessary. The adjustment of the temperature in the recording head is particularly effective for a prolonging first-ejection time because the bubble jet® type ink jet recording apparatus in which a nozzle includes a heater and this heater is heated to instantly generate air bubbles in the ink so that the pressure for generating air bubbles is used to eject ink may cause a case in which a continuous ejection operation causes a more-than-necessary temperature increase of the ink in the nozzle.
For controlling the ink temperature, a structure has been suggested in which the head includes, in addition to an ink ejection heater, a heat source such as a heat retention heater (sub heater) provided on the same substrate on which the ink ejection heater is provided. In this structure, this sub heater is driven to heat ink in a direct or indirect manner. Specifically, there is a method, for example, for detecting the ink temperature (head temperature) in a direct or indirect manner to drive the sub heater until the ink has a predetermined temperature so that power supply is interrupted when the ink has a temperature equal to or higher than the predetermined temperature and the power supply is resumed when the ink has a temperature equal to or lower than a predetermined temperature.
There is another method in which ink ejecting heaters are used to heat ink, and in which such step is repeated that power supply is performed based on a detected temperature of the recording head with a pulse width (short pulse) with which the ink is prevented from generating bubbles until the ink has a predetermined temperature and then interrupted when the ink has a temperature equal to or higher than the predetermined temperature.
Furthermore, another structure has been suggested in which the sub heater and the ejection heater are both used for controlling the ink temperature. In this structure, ink is heated by the ejection heater until the ink reaches a predetermined temperature, and once the ink has a temperature equal to or higher than the predetermined temperature, the sub heater is controlled such that the ink it further heated until the ink reaches a targeted temperature and then the resulting ink temperature is kept constant.